(a) Field of the Invention
The invention relates to a network system, particularly to a network system in which network path sharing devices tend to enter a sleep state for energy savings.
(b) Description of the Related Art
ZigBee is a specification for a suite of communication protocols using small, short-range, low-power devices based on an IEEE 802 standard for personal area networks. There are three different types of ZigBee devices—coordinator, router, and end device. Only ZigBee end devices are allowed to enter the sleep state, whereas ZigBee coordinator and ZigBee routers are not able to enter the sleep state. When an end device is too far apart from the coordinator, data collected by the end device is passed back to the coordinator in a multi-hop manner, via a path formed by a number of network path sharing devices (i.e., routers).
However, in a ZigBee network, network path sharing devices, which are responsible for maintaining a network backbone, have no sleep mechanism built in and thus cannot enter a sleep state to save energy. Even worse, without additional mechanism(s), a network path sharing device in a sleep state, if it were allowed, would make the network disconnected. Considering network path sharing devices are the nodes at large load, their power consumption is high.
Network path sharing devices deployed at a location without power outlets are usually powered by batteries. High power consumption at a network path sharing device may easily result in battery depletion. When a network path sharing device has no remaining battery capacity, the network becomes disconnected and end devices become unable to communicate to the coordinator.